This invention relates to a hydraulic system for supplying hydraulic fluid to a hydraulically operated device alternately at pressures of different values, and to a hydraulically operated device provided with such a system.
It is known to feed a liquid under pressure to a hydraulically operated device or utilizer, such as a hydraulic piston and cylinder device able to provide a mechanical force, alternately at two different pressures and particularly at a relatively low pressure and a relatively high pressure.
It is also known that in many devices, the feeding of the pressure must be as sudden as possible to achieve particular effects. As for example in a hydraulic press for manufacturing ceramic or refractory tiles, of the kind wherein the member exerting the pressing force is a hydraulic piston and cylinder, and wherein the pressing of the tiles occurs in a cycle comprising at least a first pressing step at a low pressure and a second pressing step at a high pressure, it is preferred that, at least the second pressing step is very sudden to obtain a better compactedness of the pressed material.
The known hydraulic system used to furnish the two different operating pressures are provided with two separate pumps, a first pump for supplying the low pressure, and a second one for supplying the high pressure. These known systems, at least regarding the high pressure, have the disadvantage that the installation of more than a pump with all the required conduits and fixtures is expensive, provides a greater encumbrance of the quipment and a limitation in the sudden transmission of the high pressure and the high pressure pump in particular operates with a non-linear pressure diagram, so that a remarkable loss in power takes place.